<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title></title>
  <style>
    canvas {
      box-shadow: 3px 3px 12px rgba(0, 0, 0, 0.5);
    }
  </style>
</head>
<body>
  <canvas id="canvas" width="640" height="480"></canvas>
  <script>
    const canvas = document.getElementById('canvas');
    const ctx = canvas.getContext('2d');
    
    const W = canvas.width;
    const H = canvas.height;
    
    let imgData = ctx.createImageData(200, 100);
    
    let data = imgData.data;
    
    for(let i=0; i<data.length; i+=4){
      data[i] = 255;
      data[i+1] = 255;
      data[i+3] = 255;
    }
    
    ctx.putImageData(imgData, 0, 0)
    
  </script>
</body>
</html>